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Gorge Geology Presentation Columbia Gorge Geology and the Ice Age Floods Columbia River Gorge Near Perfection... And Only 40+ Million Years in the Making Lloyd DeKay, Ice Age Floods Institute - Columbia Gorge Chapter GorgeFloods.org Geologic Time If 1 MY = 1” Dinosaurs Gone = 65in Columbia River trough = ~50in Columbia River = 20in Columbia River Basalt = 17.5-14in Ice Age Floods = .018in Earth formed = 125yd BIG BANG = 1/4mi Geology has a very long time to do its work ~50-20 MYA – Oldest Gorge Records An offshore volcanic arc, west of present-day Cascades, spewed ash eastward toward John Day Fossil Beds John Day Fossil Beds National Monument Proto-Cascades 50-20 MYA John Day Area ~30 MYA Volcanic ash from these proto-Cascade volcanos blowing eastward repeatedly buried the John Day area, preserving the world's most complete record of Miocene life Meanwhile weathered volcanic debris washed down the arc flanks into the Columbia trough Eagle Creek Debris John Day Fossil Beds Natl Monument Flow ~20MYA Columbia River Basalt 17.5-6 MYA About 17.5 MYA volcanism shifted east to the Idaho border area, burying the Columbia Basin in 1000’s of feet of basalt There were over 300 MASSIVE fissure eruptions that poured extremely fluid basalt from 20,000 vents, up to 30' wide and 10mi long • They covered 81,100mi2 to 16,000' thick • Could cover Cont. US 12'+ thick • 90% erupted in first 2 MY • 21 poured thru Columbia River “Gorge” • Flowed at up to 9mph • Took ~1 week to the coast Local Columbia River Basalt Features Stacked Basalt Layers – Horsethief Butte Basalt Arch – Catherine Creek Basalt Columns Basalt Pillows Curved Columns Horsethief Butte Pillow Basalt - Hwy 197, I-84 exit south Rise of the Cascades <3 MYA Volcanism shifted west again ~5+ MYA Columbia River downcut as the Cascades slowly rose Shield Volcanoes Began <1MYA These were broad, low relief volcanos, similar to Hawaiian Island volcanos Mt Defiance @ sunset Frosty Underwood Mtn Strato-Volcanoes Began ~500,000 YA Mt Adams Their stiffer lavas tend to build upward Mt Hood Local Cascades Features Folded CRB – Coyote Wall, SR14 east of Bingen Bird Crk Meadows – Mt Adams Lava Tubes – Guler Ice Caves, Trout Lake Collapsed Lava Tubes – White Salmon River Missoula/Spokane/Bretz Floods At the end of the ice ages,18-12 KYA, ice dams repeatedly blocked the Clark Fork River creating Glacial Lake Missoula When the ice dams broke they released massive floods across central WA and all the way to the Pacific Ocean Release of Cataclysmic Floods Maybe 120 times (~every 50 years) these Ice dams broke catastrophically, releasing huge floods up to 1000' deep that raced at up to 60 mph across central WA, through Wallula Gap, the Gorge, and on to the Pacific Ocean The lake floated and undermined the ice dam, causing catastrophic collapse The floods swept away icebergs carrying encased rock that later melted out downstream as erratics. Floods Across the Landscape Stev Ominski 140 mi3/day poured across the eastern WA landscape It striped sediment and plucked massive blocks of bedrock behind a wall of water up to 1000’ high. It could have been felt 2 hours beforehand. It left behind massive coulees, scablands, mega- ripples and bars, even lake Dry Falls deposits. Evidence Left Behind Touchet Lake Beds Deposited inTemporary Lakes Mega-Ripples 30+ ft high (Camas Prairie) Massive Rolled Basalt Boulders Huge Coulees and Scablands Through Wallula Gap Wallula Gap only allowed ~40 mi3/day, forming a large temporary Lake Lewis behind it reaching into the Yakima Valley Narrower channels downstream caused more temporary lakes. Modelling shows it took a month for each flood to fully drain And On Through the Gorge Remember, the Gorge was already here… for the past 20 million years Stev Ominski The floods swept away the erosional debris, leaving behind the majestic palisades and waterfalls of the Columbia Gorge National Scenic Area Columbia River Gorge Peter Marbach Some Local Features Whirlpools plucked bedrock Kolk Pond at The Dalles Discovery Center Erratics and Huge Gravel Deposits Mark Hatfield, Mosier Streamlined Bedrock Outcrops Horsethief Butte, WA Turbulent Water-Cut Benches opposite Dalles Discovery Center Scablands at Columbia Hills State Park, WA Hanging Valleys with Upstream Dipping Foreset Beds Spectacular Gorge Waterfalls (Canyon Road, Lyle) like Multnomah Falls off I-84 Missoula/Spokane/Bretz/Ice Age Floods A MAJOR Geologic Controversy Challenged by Six Geology Elders W. C. Alden Henry Ferguson Oscar E. Meinzer E. T. McKnight James Gilluly G. R. Mansfield James Gilluly Oscar E. Meinzer The Elders fought Bretz’s “heretical” neo-Catastrophist explanation until Joseph T. Pardee’s 1940 Glacial Lake Missoula presentation that provided the source for the floods and ended J Harlan Bretz the debate Neo-Catastrophist in 1923 Joseph T. Pardee Proposed a megaflood explanation, but not where floods came from Landsat Confirmation Bretz’s theory was fully confirmed on Landsat images Landsat Image (1970s) Bretz Map (1930s) More Recent Gorge Geology Bonneville Dam Bonneville Landslide ~1450 A.D. Bridge of the Gods Indian Legend Loowit (Mt St Helens) Pahtoe (Mt Adams) Wy’east (Mt Hood) 40+ Million Year Recap Cascades, Ice Age Floods, and Columbia River Gorge Mt Washington Columbia River Basalts Proto-Cascades Ice Age Floods National Geologic Trail Still a few years off, it will be under the National Park Service .
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